We investigate the link between birth order and the career outcome of becoming Chief Executive Officer (CEO) of a company. We find that CEOs are more likely to be the first-born, i.e., oldest, child of their family. This result holds for family firms, where traditionally the oldest child is appointed to run the family business, but also for non-family firms. We also find that CEOs are significantly less likely to have older brothers (relative to younger brothers) than older sisters (relative to younger sisters). The advantage of being first-born seems to decay over time, consistent with changing family structures and rearing practices as well as changing social norms.